Measuring circuit is composed of monostable oscillator ( 4538 ), the divider ( 4024), pulse generator ( ICM7555 ), counter ( 4040), latch ( 74HC513 ), memory ( ROM ), seven-segment latch drive ( 7511 ) and seven-segment digital LED tube. Figure (a) is a structural diagram of the PVDF heart sound pulse sensor. In Figure ( a ), PVDF film is dome-shaped and slightly protruding outward to make a good contact with the skin surface. The PVDF material is flexible to close to the skin, the impedance is matching with the skin, subsequently, even under stress, the pressure does not affect the detection pulse pressure variation, and therefore able to detect a slight ripple signal.
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